Fuel Cell Stack Assembly: From Gemini to ABB Robots

Fuel cell stack assembly means placing hundreds of thin bipolar plates, membrane electrode assemblies and seals on top of each other, in exact alignment, then pressing the pile into one block. A single slip causes a leak between hydrogen and air. This post follows the job from the hand-built cells of the space programme to Toyota's 370-cell Mirai stack, then looks at the new heavy-duty stacks EKPO and Symbio showed at IAA Transportation 2026, where ABB robots such as the IRB 2600 already stack cells, and what has to change before stacks are built in the hundreds of thousands.

The fuel cell stack of a Toyota Mirai, shown in a cutaway car at the São Paulo motor show in 2016. Photo: Mariordo (Mario Roberto Durán Ortiz) / Wikimedia Commons (CC BY-SA 4.0)

How fuel cells went from lab benches to hand-built stacks

The fuel cell is older than the car. William Grove described his first hydrogen cell in 1838, and in 1959 the British engineer Francis Thomas Bacon showed a practical 5 kW unit that could power a welding machine. At General Electric, W. Thomas Grubb used an ion-exchange membrane as the electrolyte in 1955, and Leonard Niedrach found a way to deposit platinum onto it three years later. The Grubb-Niedrach cell powered the Gemini spacecraft on ten missions in 1965 and 1966, the first commercial use of a fuel cell.

A cutaway of the General Electric fuel cell used on Gemini spacecraft in 1965 and 1966. Photo: General Electric Co. via Wikimedia Commons (CC0)

Before robots, stacks were put together by hand, one part at a time. A cell is a membrane electrode assembly between two plates, and cells are stacked in series to reach a useful voltage, so every extra cell adds parts to align. A 2017 review by Vladimir Gurau and colleagues at Georgia Southern University cited estimates of 0.64 to 0.83 minutes per cell for manual assembly. It also noted that misaligned plates, membranes or gaskets cause leaks to the outside or between anode and cathode.

Fuel cells installed in a fuel cell powered bus, photographed by NASA in January 1995. Photo: NASA Armstrong Flight Research Center via Wikimedia Commons (public domain)

Researchers tried robots on the job once fuel cell cars looked possible. University groups built test cells with KUKA and Fanuc arms, and the German institutes ZSW and ZBT demonstrated assembly lines that applied liquid rubber seals straight onto plates and membranes. In one comparison a 20-cell stack took about 50% longer to build by hand than with a robot. Toyota put the Mirai on sale in December 2014. Its first-generation stack held 370 cells, each 1.34 mm thick, and delivered up to 114 kW.

A Toyota Mirai cutaway with its fuel cell stack under the seats and its hydrogen tanks behind. Photo: Mariordo (Mario Roberto Durán Ortiz) / Wikimedia Commons (CC BY-SA 4.0)

Heavy-duty stacks designed for robots in 2026

The newest stacks are designed around the production line. At IAA Transportation in Hanover in September, EKPO, the joint venture of ElringKlinger and OPmobility, showed the next stage of its NM20 stack. EKPO says it revised the design from the bipolar plate to the housing to improve automatability, quality assurance and traceability. The single-stack module has 323 cells and more than 200 kW, the twin-stack module 646 cells and more than 400 kW. The module is about 20% smaller than before and weighs 178 kg, 39 kg less. EKPO also built cell voltage monitoring, water separation and the high-voltage connection into the stack itself, which leaves fewer separate parts to fit later.

A hydrogen fuel cell truck on show at IAA Transportation in Hanover, 2024. Photo: Matti Blume / Wikimedia Commons (CC BY-SA 4.0)

Symbio, at the same show, presented its third-generation stack with a new bipolar plate that doubles the active surface and a new compression design. The stack goes into a 150 kW StackPack system with a volume of 80 litres and a weight of 90 kg, and B-samples reach customers in January 2027. It will be built at SymphonHy in Saint-Fons, France, a 26,000 m² plant that runs from catalyst ink to finished systems. Symbio says the plant has already built 100 systems a week and should reach 10,000 systems a year.

An ABB robot with a large gripper above a pile of stack plates in Siemens Energy's Berlin factory. Photo: Siemens Energy

ABB robots already do parts of this work. The Manufacturer described a fuel cell assembly cell built around an ABB IRB 2600, an arm with 1.65 m of reach and 20 kg of payload, inside a racked enclosure of component hoppers. Its gripper finds the top of each hopper's pile, records the position and then picks plates and electrodes at speed. ABB also lists welding and sealing for stack components, and its Integrated Dispensing Function Package for gluing. Siemens Energy uses ABB robots on its electrolyzer stack line in Berlin, a close relative covered in our post on electrolyzer manufacturing.

An ABB IRB 2600, the arm used in a fuel cell stack assembly cell, here handling face mask parts. Photo: ABB

What fuel cell stack lines need over the next decade

Volume is the next problem. A stack with 323 or 646 cells means several hundred plates and membranes per stack, and lines built for 10,000 systems a year must place them in seconds and without damage. Membranes are thin and easily creased, and plates can warp. The Georgia Southern review found that rigid steel alignment pins did not work well with robots that have limited accuracy and no joint flexibility, and that flexible pins and grippers with passive compliance gave better results. That give soaks up small errors from warped parts and from the robot's own limited accuracy.

A Higher fuel cell box truck, model KLQ5180XXYFCEV, on a city street. Photo: JustAnotherCarDesigner / Wikimedia Commons (CC0)

That points to robots with vision and force feedback. A fast ABB picker such as the IRB 360 FlexPicker could feed small plates, while larger arms like the IRB 2600 or IRB 4600 place them on the stack and check alignment with a camera. ABB has not announced such a line for EKPO or Symbio, so this is a possible layout. Cells like these are usually built and tested first in RobotStudio, where an engineer can check reach and cycle time before ordering hardware.

ABB robot arms on the electrolyzer stack line at Siemens Energy in Berlin. Photo: Siemens Energy

Cost and skills are still open. EKPO's NM20 work has public support of up to 177 million euros through the European IPCEI programme. Stack lines also need staff who understand both electrochemistry and automation, since a misplaced gasket only shows up later as a leak in the finished stack. Outside trucks, EKPO and Symbio both pitch their stacks for stationary power, such as backup systems and generator sets, which is where fuel cells come closest to homes and offices.

An ABB robot working over battery modules in the cell at ABB's Baden plant. Photo: ABB

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